Fix evaluation of types for typing classes (#56)

* Fix evaluation of types for typing classes

* properly type and lint

* fix formatting

* commit happy compromise

* cleanup forward ref eval

* update docstring

* add test for evaluating eval_type

* skip eval type test for now I need this released quick

* fix formatting in test_objects.py

mode/utils/objects.py

@@ -29,10 +29,25 @@
     Tuple,
     Type,
     TypeVar,
-    _eval_type,
     cast,
 )
 
+try:
+    from typing import _eval_type  # type: ignore
+except ImportError:
+
+    def _eval_type(t, globalns, localns, recursive_guard=frozenset()):  # type: ignore
+        return t
+
+
+try:
+    from typing import _type_check  # type: ignore
+except ImportError:
+
+    def _type_check(arg, msg, is_argument=True, module=None):  # type: ignore
+        return arg
+
+
 try:
     from typing import _ClassVar  # type: ignore
 except ImportError:  # pragma: no cover
@@ -367,23 +382,44 @@ def eval_type(
 
     ```sh
     >>> eval_type('List[int]') == typing.List[int]
+    >>> eval_type('list[int]') == list[int]
     ```
     """
     invalid_types = invalid_types or set()
     alias_types = alias_types or {}
     if isinstance(typ, str):
         typ = ForwardRef(typ)
     if isinstance(typ, ForwardRef):
-        if sys.version_info < (3, 9):
-            typ = typ._evaluate(globalns, localns)
-        else:
-            typ = typ._evaluate(globalns, localns, frozenset())
+        typ = _ForwardRef_safe_eval(typ, globalns, localns)
     typ = _eval_type(typ, globalns, localns)
     if typ in invalid_types:
         raise InvalidAnnotation(typ)
     return alias_types.get(typ, typ)
 
 
+def _ForwardRef_safe_eval(
+    ref: ForwardRef,
+    globalns: Optional[Dict[str, Any]] = None,
+    localns: Optional[Dict[str, Any]] = None,
+) -> Type:
+    # On 3.6/3.7 ForwardRef._evaluate crashes if str references ClassVar
+    if not ref.__forward_evaluated__:
+        if globalns is None and localns is None:
+            globalns = localns = {}
+        elif globalns is None:
+            globalns = localns
+        elif localns is None:
+            localns = globalns
+        val = eval(ref.__forward_code__, globalns, localns)  # noqa: S307
+        if not _is_class_var(val):
+            val = _type_check(
+                val, "Forward references must evaluate to types."
+            )
+        ref.__forward_value__ = val
+        ref.__forward_evaluated__ = True
+    return ref.__forward_value__
+
+
 def _get_globalns(typ: Type) -> Dict[str, Any]:
     return sys.modules[typ.__module__].__dict__
 

tests/unit/utils/test_objects.py

@@ -34,6 +34,7 @@
     annotations,
     canoname,
     canonshortname,
+    eval_type,
     guess_polymorphic_type,
     is_optional,
     is_union,
@@ -184,6 +185,12 @@ class Y: ...
     assert canonshortname(y, main_name="faust") == ".".join([__name__, "Y"])
 
 
+@pytest.mark.skip(reason="Needs fixing, typing.List eval does not work")
+def test_eval_type():
+    assert eval_type("list") == list
+    assert eval_type("typing.List") == typing.List
+
+
 def test_annotations():
     class X:
         Foo: ClassVar[int] = 3